Horizon
Definition
- The horizon is the line that separates the Earth from the sky.
Types of Horizons
Earth-Sky Horizons
- Local Horizon (Geometrical Horizon): Visible boundary including trees, buildings, mountains.
- Geographic Horizon: Apparent boundary excluding elevated features like mountains, trees.
- Sea-Level Horizon: Geographic horizon at sea level, best observed from a beach. The offing is where the sea "touches" the horizon.
Celestial Horizons
- Astronomical Horizon: Imaginary horizontal plane at a 90-degree angle from the observer's zenith. It forms great circles around the observer.
- True Horizon: Imaginary plane passing through Earth's center, perpendicular to its radius, appearing spherical from orbit.
Importance of the Horizon
- Aviation: Pilots use the horizon for "attitude flying" to maintain level flight.
- Navigation: Before modern tools, sailors used the horizon for navigation and determining the time of day via the sun's position.
- Celestial Navigation: Stars and constellations, like the Southern Cross, helped sailors navigate by rising and setting on the horizon.
- Art: Artists use the horizon to create perspective and depth in paintings and drawings.
- Communication: Before radio and telegraph, communication was limited to the local horizon.
Historical Significance
- Flat Earth Belief: Persisted until the late Middle Ages; the horizon was seen as the edge of the Earth.
- Proof of Earth's Sphericity: Aristotle observed that constellations rose higher from the horizon when moving south, indicating a spherical Earth.
Additional Information
- Media Credits: Media assets are credited under each media item unless promotional.
- Latest Update: October 19, 2023
User Permissions and Media
- Text is printable under the Terms of Service.
- Interactives are only available on the website.
For more detailed information, the full article can be accessed on National Geographic.